Title of Invention

ELECTRODE CAPABLE OF STORING HYDROGEN AND A METHOD FOR THE PRODUCTION OF THE SAME

Abstract

An electrode which has the capacity to store hydrogen, having a metallic substrate material, to which an active compound is applied, characterised in that the active compound is obtainable from a paste which comprises a dry fraction and a liquid fraction, the dry fraction comprising a mixture of a pulverulent storage alloy for hydrogen, soot and polytetrafluoroethylene (PTFE), the particles of the storage alloy being covered with PTFE in the manner of fibrils, and the liquid fraction comprising a mixture of water and a higher alcohol which has from 3 to 6 C atoms.

Full Text

FORM 2 THE PATENTS ACT 1970 [39 OF 1970] & THE PATENTS RULES, 2003 COMPLETE SPECIFICATION [See Section 10; rule 13] 'ELECTRODE CAPABLE OF STORING HYDROGEN AND A METHOD FOR THE PRODUCTION OF THE SAME' DEUTSCHE AUTOMOBILGESELLSCHAFT MBH, a German company of Gifhorner Strasse 57, D-38112 Braunschweig, Germany, The following specification particularly describes the invention and the manner in which it is to be performed: The present invention relates to an electrode with a capacity to store hydrogen, having a metallic substrate material to which, an active compound is applied. The present invention also relates to a method for producing an electrode of this type. An electrode of the generic type is described in DE 37 02 138 Al. This document discloses an electrode which has a capacity to store hydrogen, for carrying out electrochemical and chemical reactions, which comprises a mixture of Raney nickel powder and the powder of at least one hydrogen storage alloy, the grains of which are covered with fibrillated polytetrafluoroethylene (PTFE). The Raney nickel and alloy grains are compressed by rolling or pressing in such a manner that they form a cohesive, electronically conductive body and are held together by the PTFE fibril network which is located in the interstices. In an electrochemical cell, two pore systems which link up with one another are formed inside the electrode body of this electrode, one of which systems contains the electrolyte and comprises the packing gaps between the Raney nickel grains and the grains of the hydrogen storage alloy and the other of which is formed from the cohesive interstices of the Raney nickel grains and is not flooded by the electrolyte on account of the hydrophobic action of the PTFE. Therefore, this pore system contains hydrogen. This document also mentions what are described as plastic-bonded hydrogen storage electrodes which are produced, for example, in accordance with DE-A 27 27 200 from the powder of a hydrogen storage alloy, for example the nickel-titanium or nickel-lanthanum system, and PTFE as binder in a kneading process. A drawback of this arrangement is that although efficient electrochemical charge storage is possible, it is associated with a deterioration in the power capacity or function, i.e. with a dragging gas conversion. This is presumably linked to the non-porous, hydrophobic nature of the electrode structure, so that the electrochemical exchange between electrolyte solution and the alloy phase no longer functions perfectly. However, the Raney nickel component reduces the specific storage capacity of this known electrode compared to the plastic-bonded storage electrode again. However, it is desired to use electrodes with a particularly high specific storage capacity in storage batteries. Therefore, the object of the present invention is to provide an electrode of the abovementioned type which has a particularly good specific storage capacity and a good power capacity. The further object is to provide a method for producing an electrode of this type which is simple, rapid and inexpensive. The solution consists in an electrode having the features of claim 1 and a method having the features of claim 8. Therefore, according to the invention, it is provided that the active compound is obtainable from a paste which is composed of a dry fraction and a liquid fraction. As well as a hydrogen storage alloy and PTFE, the dry fraction also contains soot; the liquid fraction contains water and an alcohol which has 3-6 C atoms, the particles of the storage alloy being covered with PTFE in the manner of fibrils. The addition of soot is important to make the mixture easier to process. The addition of soot makes the mixture pasty and able to flow. In the electrode, the soot promotes the electrical contact on a microscale (up to approximately 500 μm), i.e. it spans the distances and provides electrical contact between the openings or pores in the substrate material. These distances or openings, with a size of up to 500 μm, cannot be bridged by the particles in the paste or the active compound which can be obtained therefrom, since they generally have a diameter of only approximately 10 to 100 μm. Furthermore, the soot serves as an oxygen gate for protecting the oxygen-sensitive storage alloy. The PTFE is responsible for the hydrophobic properties of the electrode and enables the three-phase boundary to be set. The reduction of the oxygen and the release and uptake of the hydrogen in the working cell take place in the only partially wetted pores. The PTFE is also responsible for enabling the paste to flow and hold together in the mixing or shaping process. The alcohol is in turn responsible for the temporary wetting of the PTFE powder, since otherwise there would be no distribution through fibrillation in the mixing process. In this way, the properties of the plastic-bonded storage electrodes with their high specific storage capacity and the properties of the electrodes with a mixture of storage alloy and Raney nickel powder, with their good power capacity or operation, are combined. The method for producing the electrode according to the invention is very simple. The components are mixed in a mixer until a cohesive paste is formed. The paste is shaped and combined with the metallic substrate material (for example expanded metal, fabric, grid, perforated sheet) of the electrode. This is an extraordinarily simple process sequence. The electrode according to the invention means that it is also no longer necessary, in conventional plastic-bonded storage electrodes, to use a PTFE dispersion with a high wetting agent content, which has to be removed by decomposition at elevated temperature {300°C), damaging the storage alloy. Advantageous refinements will emerge from the subclaims. The dry fraction contains 85-95 parts of the storage alloy, approximately 2-10 parts of soot and 3-8 parts of PTFE. The liquid fraction contains 30-70 parts by volume of water and 70-30 parts by volume of the alcohol. Alcohols' with a boiling point of the order of magnitude of 100°C, i.e. for example n-butanol or n-propanol, are particularly suitable. Furthermore, polyethylene glycol may be included in the liquid fraction. The PTFE component means that the finished electrode can only be wetted by lye with extreme difficulty. Therefore, to achieve a sufficient uptake of electrolyte, a polyethylene glycol can be supplied with the make-up water. The proportion of polyethylene glycol is 0.05-0.2% (based on the dry fraction) . It is preferable to use a polyethylene glycol with a molecular weight of between 105 and 5xl06 g/mol. The alcohol used is preferably n-propanol or n-butanol. Depending on the soot content, the ratio of the dry fraction to the liquid fraction is between 4:1 and 6:1, based on mass. The electrode according to the invention is preferably used in an alkaline storage battery with positive nickel oxide electrode. The electrode according to the invention is produced by rolling a dough-like paste onto a structured metal substrate, such as for example an expanded metal or grid mesh. The dough-like paste is prefabricated in a first production step by a mixing and kneading process. The solid and liguid components are mixed in a kneading machine until a cohesive paste is formed, for example in a stable domestic kneading machine. The PTFE particles are fibrillated by the hard compound grains and hold the paste together. The electrode is shaped either by manual rolling or in a rolling train. Either a sheet is produced and is combined with the substrate after drying or the kneaded compound is applied directly to the substrate and is then dried. The text which follows describes an exemplary embodiment of the present invention in more detail. The following components were mixed together with water in order to produce a paste or pasty compound which can be rolled: - 68% by mass of commercially available hydrogen storage alloy (lanthanum/misch-metal/nickel alloy with a grain size of less than 90 μm)/ 3.8% by mass of acetylene black (soot) (specific surface area 50-80 m2/g); 3.8% by mass of PTFE powder (grain size less than 50 μm); 10.9% by mass of n-propanol. High-molecular-weight polyethylene glycol (for example with a molecular weight of 5x10s g/mol) was dissolved in the added water in a concentration of 0.65% by mass. This mixture was kneaded and mixed for 3 min in a domestic kneading machine. During this operation, the compound forms into a ball and can be fed to the rolling operation. A sheet with a thickness of 1 mm was produced on a bench roller. This sheet web was dried in a vacuum drying cabinet at 100°C. The dried sheet web was applied to a substrate material (nickel mesh 'or expanded grid made from nickel or nickel-plated copper) by rolling (double roller with, a nip setting of 0.4 mm) . The finished electrode had, a final thickness of 0.5 mm. With an application of coating of 0.17 g/cm2, the electrode, when operated as a hydrogen storage electrode in 6 M KOH, has a capacity of 43 mAh/cm2. WE CLAIM: 1. An electrode which has the capacity to store hydrogen, having a metallic substrate material, to which an active compound is applied, characterised in that the active compound is obtainable from a paste which comprises a dry fraction and a liquid fraction, the dry fraction comprising a mixture of a pulverulent storage alloy for hydrogen, soot and polytetrafluoroethylene (PTFE), the particles of the storage alloy being covered with PTFE in the manner of fibrils, and the liquid fraction comprising a mixture of water and a higher alcohol which has from 3 to 6 C atoms. 2. The electrode as claimed in claim 1, wherein the dry traction has 85 to 95 parts of the storage alloy for hydrogen, 2 to 10 parts of soot and 3 to 8 parts of PTFE. 3. The electrode as claimed in any one of the preceding claims, wherein the liquid fraction contains 30 to 70 parts by volume of water and 70 to 30 parts by volume of the alcohol, as well as 0.05 to 0.2% (based on the dry fraction) of PEG. 4. The electrode as claimed in any one of the preceding claims, wherein the liquid fraction also contains polyethylene glycol (PEG). 5. The electrode as claimed in claim 4, wherein the PEG has a molecular weight of between 105 and 5xl06g/mol. 6. The electrode as claimed in any one of the preceding claims, wherein the liquid fraction contains n-propanol and/or n-butanol as alcohol. 7. The electrode as claimed in any one of the preceding claims, wherein the mass ratio of the dry fraction to the liquid fraction is 4:1 to 6:1. 8. A method for producing the electrode with storage capacity as claimed in any one of claims 1 to 7, wherein a dry fraction comprising a mixture of a storage alloy for hydrogen, soot and polytetrafluoroethylene (PTFE) and a liquid fraction comprising a mixture of water and a higher alcohol which has 3 to 6 C atoms are used, the dry fraction and the liquid fraction are mixed in a kneading machine until a cohesive paste is formed, and the resulting paste is combined with a metallic substrate material and is dried. 9. The method as claimed in claim 8, wherein a mixture comprising 85 to 95 parts of the storage alloy for hydrogen, 2 to 10 parts of soot and 3 to 8 parts of PTFE is used as the dry fraction. 10. The method as claimed in any one of claims 7 to 9, wherein a mixture comprising 30 to 70 parts by volume of water and 70 to 30 parts by volume of the alcohol, as well as 0.05 to 0.2% (based on the dry fraction) of PEG is used as the liquid fraction. 11. The method as claimed in any one of claims 7 to 10, wherein a mixture which also contains polyethylene glycol (PEG) is used as the liquid fraction. 12. The method as claimed in claim 11, wherein PEG with a molecular weight of between 105 and 5xl06 g/mol. is used. 13. The method as claimed in any one of claims 8 to. 12, wherein n-propanol and/or n-butanol is used as alcohol. 14. The method as claimed in any one of claims 8 to 13, wherein the dry fraction and the liquid fraction are mixed in a mass ratio of 4:1 to 6:1. 15. The method as claimed in any one of claims 8 to 14, wherein the resulting paste is compressed to form a sheet, preferably by rolling, and this sheet, after drying, is combined as active compound with the substrate material. 16. The method as claimed in any one of claims 8 to 14, wherein the resulting paste is applied directly to the substrate material, preferably by rolling, and is then dried in order to obtain the active compound. 17. The use of the electrode as claimed in any one of claims 1 to 7 as negative electrode in alkaline storage batteries with positive nickel oxide electrode. Dated this 7th day of January, 2002 [JAYANTA PAL] OF REMFRY & SAGAR ATTORNEY FOR THE APPLICANTS

Documents:

abstract1.jpg

in-pct-2002-00023-mum-cancelled pages(17-06-2005).pdf

in-pct-2002-00023-mum-claims(granted)-(17-06-2005).doc

in-pct-2002-00023-mum-claims(granted)-(17-06-2005).pdf

in-pct-2002-00023-mum-correspondence(28-03-2006).pdf

IN-PCT-2002-00023-MUM-CORRESPONDENCE(8-2-2012).pdf

in-pct-2002-00023-mum-correspondence(ipo)-(05-04-2007).pdf

in-pct-2002-00023-mum-declaration(07-01-2002).pdf

in-pct-2002-00023-mum-drawing(17-06-2005).pdf

in-pct-2002-00023-mum-form 19(19-04-2004).pdf

in-pct-2002-00023-mum-form 1a(17-06-2005).pdf

in-pct-2002-00023-mum-form 2(granted)-(17-06-2005).doc

in-pct-2002-00023-mum-form 2(granted)-(17-06-2005).pdf

in-pct-2002-00023-mum-form 3(12-04-2004).pdf

in-pct-2002-00023-mum-form 3(24-06-2005).pdf

in-pct-2002-00023-mum-form 5(07-01-2002).pdf

in-pct-2002-00023-mum-form-pct-ipea-409(17-06-2005).pdf

in-pct-2002-00023-mum-form-pct-isa-210(17-06-2005).pdf

in-pct-2002-00023-mum-petition under rule 137(24-06-2005).pdf

in-pct-2002-00023-mum-power of authority(17-06-2005).pdf

in-pct-2002-00023-mum-power of authority(18-01-2002).pdf